This invention relates generally to x-ray generating equipment, and more particularly to methods and apparatus for maintaining an electron beam incident angle and focus on an x-ray target anode.
In medical x-ray imaging, an x-ray tube is utilized for generating x-ray beams that pass through an object being imaged. More specifically, an x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as an “imaging plane”. The x-ray beam passes through an object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at a detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged, so the angle at which the x-ray beam intersects the object constantly changes. X-ray sources typically include x-ray tubes, which emit the x-ray beam at a focal spot. X-ray detectors typically include a collimator for collimating x-ray beams received at the detector, a scintillator adjacent the collimator, and photodetectors adjacent to the scintillator.
Known x-ray tubes include a cathode aligned with a rotating target anode. An electron beam generated at a cathode emitter is directed towards the anode and forms a focal spot on an anode surface. As a result, x-ray beams are emitted from the anode.
The shape and focus of the electron beam emitted from the cathode emitter are defined by the cathode. In spite of the shaping and focusing within the cathode, as the beam travels to the anode, electric fields within the x-ray tube can accelerate the electrons and possibly even deflect and defocus the beam. If the electron beam does not have the desired shape and focus, the resulting x-ray beam also will lack such characteristics. As a result, the image quality of an image generated based on projection data collected utilizing such x-ray beams may not be as high as desired.